#sidebar {
    width: 280px;
    height: 100%;
    background-color: #cccccc8c;
    float: left;
}
#sidebar ol {
padding: 0 30px;
}

#container {
    width: calc(100% - 280px);
    height: 100vh;
    background: #eee;
    float: left;
}

.theme1 {
    background: red;
}
.theme2 {
    background: green;
}
.theme3 {
    background: blue;
}